Tighten monthly release validation

[Pigbibi]

Summary

• reject latest_ranking.csv selected_flag counts that differ from live_pool.json symbols length
• remove manual GITHUB_OUTPUT override from monthly_publish.yml
• add focused regression coverage for both issues found by the post-merge Codex review

Verification

• ~/.cache/crypto-codex-audit/python-venv/bin/python -m unittest tests.test_release_contract tests.test_release_status_summary tests.test_monthly_review_briefing tests.test_monthly_publish_workflow_config tests.test_monthly_report_bundle
• ~/.cache/crypto-codex-audit/python-venv/bin/python -m compileall -q scripts src tests